Exxon Mobil Corp. has agreed to disclose how the costs of carbon emissions could affect its business model and the worth of its fossil fuel reserves, a wealth management group with a focus on green portfolios said Thursday.

“Shareholder value is at stake if companies are not prepared for a low-carbon scenario,” Natasha Lamb, director of equity research at Arjuna Capital, said in a written statement.

Arjuna and As You Sow, an investment group promoting “social corporate responsibility,” had pushed for shareholder resolutions endorsing what they call a carbon asset risk report.

It's the first time that Irving-based Exxon Mobil Corp., the nation's largest oil company, has agreed to tell investors how it appraises carbon-intensive assets such as oil sands under increasingly strict climate rules.

Investors are pushing for similar commitments from nine other energy producers, including Anadarko Petroleum, Chevron, Devon Energy and Hess.

Exxon Mobil declined to comment, but email exchanges between Lamb and company spokesman David Rosenthal, obtained by the Houston Chronicle, show that Arjuna withdrew the shareholder proposal in exchange for Exxon Mobil's commitment.

“We are in agreement to proceed with your withdrawal of the Shareholder Proposal, and our producing the comprehensive report on Carbon Asset Risk,” Rosenthal wrote.

“We are very pleased with your commitment to write a report and address our concerns,” Lamb wrote in an email dated March 17.

The activist shareholders pushing for the carbon asset risk reports say that in 2012, public energy producers spent $674 billion on exploring and developing new reserves they can't burn without causing what the shareholders term “catastrophic” global warming.

“More and more unconventional 'frontier' assets are being booked on the balance sheet, such as deep water and tar sands,” Lamb said. “These reserves are not only the most carbon intensive, risky and expensive to extract, but the most vulnerable to devaluation.”

Those reserves are valued at $20 trillion on 200 of the largest energy companies' balance sheets, the investors said, but only a third of those reserves could be used before carbon emissions cause crippling climate change.

Late last year, a collection of well-heeled investors with $3 trillion in assets under management formed the Carbon Asset Risk Initiative to press oil, gas and coal companies to publish regular reports on reserves they consider high risk because of their concentration of carbon.

The group coordinated investor letters to energy companies last fall.

In an interview with the Chronicle, Arjuna Capital's Lamb said Exxon Mobil could start publishing the carbon risk report as early as the end of this month. The investors then plan to push the company to begin divesting from the riskiest assets, such as carbon-intensive oil sands and deep-water projects, and return money to shareholders instead.

But Exxon Mobil isn't likely to start selling off its prospects anytime soon, said Brian Youngberg, an analyst with Edward Jones.

“It's hard for a company of Exxon's size to continue to invest and avoid deep water, shale and oil sands; those are the three growth areas in the sector,” Youngberg said.

And other oil companies likely will keep resisting activist calls to drop their investments in carbon-heavy projects, said Fadel Gheit, an analyst with Oppenheimer & Co.

Chevron spokesman Justin Higgs said only that the proxy statement the company issues ahead of its annual shareholders' meeting “will contain the board of directors' response to the stockholder proposal received by the company.”